Hi, Its really an interesting Project and many people can benefit from it.
To start off and get a better idea of how things will work, you can use amazon AWS servers, as they provide one year of free service and that would be more than enough to make this project a reality.
So, the Idea is to create few instances of EC2 cloud service and make them work together in sync. This will save your trouble of using raspberry pi and its more powerful than a raspberry pi with better internet connectivity, all for free.
Take a look herehttps://console.aws.amazon.com/console/home?region=us-east-1
I can help with the setup.
I will be glad to help, as my expertise fall into this domain. Currently I am using amazon aws EC2 cloud service.